Dental crown, coping and method

ABSTRACT

The dental jacket crown of the present invention is prepared from a thin metal foil substrate which is coated with a noble based metal composition having a low fusing temperature and folded in a predetermined manner to form a multiple number of triangular like flaps or pleats. The folded foil represents the coping of the present invention. The coping is mounted over a die of the prepared tooth and the flaps wrapped in overlapping formation and then adapted to the die. The die is removed and the structure heated preferably under a bunsen burner. A veneering material such as porcelain is then coated over the structure to form the crown.

This invention relates to the field of dental restorations and moreparticularly to the jacket crown restoration, a jacket crown coping fora jacket crown restoration and to a method for forming a jacket crown.

Dental porcelain, a conventional material composed of a mixture ofheldspar, quartz and kaolin is commonly used in fabricating dentalrestorations. The most prevalent crown construction for dentalrestorations is the porcelain veneer cast metal crown. The cast metalcrown is fabricated using a relatively thick metal understructure formedfrom casting an investment of a wax or plastic pattern of the preparedtooth. Dental porcelain is then applied in layers over part or all ofthe understructure and fired at high temperature to form a veneer. Themetal understructure is preferably formed from a noble based metal oralloy predominantly of gold. The thickness of the cast metalundersturcture ranges from typically 0.3 to 0.5 mm. The cast metalunderstructure is expensive and particularly so for a noble based metalunderstructure. The weight of a precious metal cast crown is from one tothree grams. Since the bulk of the restoration is no greater than thatof the tooth structure which originally occupied the space, the use of athick metal understructure minimizes the permissible thickness for thetranslucent porcelain veneer. Moreover, exposure of the metalunderstructure will detract from the esthetics of the restoration.

It is well known that the full porcelain or porcelain jacket crown isesthetically superior to all other crown restorations and is virtuallyimpossible to visually distinguish from a natural tooth. Accordingly, itshould be commonplace but is, in general, indicated for use only as afull coverage for an anterior tooth where esthetics is the primeconsideration. The limited use of the porcelain jacket crown isattributable to its present method of construction with the strength ofthe jacket crown dependent upon the strength of the porcelain materialcomposition. Porcelain is inherently structurally weak and fragile. Inaddition, the present day method of construction requires a high degreeof proficiency to establish accurate marginal fit and finish and toavoid poor seating of the crown occlusally relative to the preparation.An improper fit at the gingival margin results in a cement line whichreadily washes away inviting decay and loosening the crown attachment.

In the conventional process for preparing a porcelain jacket crown aplatinum foil is swaged about the prepared die of the tooth to form amold substrate upon which the porcelain may be fired. The foil is thenremoved from the substrate before the crown is cemented to the toothpreparation. The latter requirement is considered a principle failing ofthe conventional porcelain jacket crown preparation. An improvedporcelain jacket crown construction in which the swaged foil substrateis itself included as an integral component of the finished porcelainjacket crown is taught and described in U.S. Pat. No. 4,273,580 issuedto the Applicants herein, the disclosure of which is herein incorporatedby reference. In the latter patent the metal foil substrate forms thecore of the jacket crown. A coating of a predetermined noble based metalcomposition is sintered to the foil substrate whichis then adapted tothe die in a manner similar to that in the conventional preparation of aporcelain jacket crown. Although this jacket crown construction willexhibit substantially improved physical properties, its method ofconstruction is still dependent upon the skill and dexterity of asuperior dental technician.

The present invention utilizes an entirely new technique forconstructing a porcelain jacket crown which overcomes all of theshortcomings of the conventional porcelain jacket crown in mechanicalproperties, construction and preparation. In fact the preformed copingof the present invention is readily adaptable by a technical novicewithout any special skills. Use of the preformed coping in accordancewith the presesnt invention simplifies construction of a porcelainjacket crown and significantly contributes to uniformity in resultwithout the dependency on the skill of the dental technician.

The porcelain jacket crown of the present invention may be prepared morequickly and more accurately relative to conventional methods ofpreparation. Moreover, the dental laboratory does not have to wax,invest, cast or polish the final metal structure as is done in making aporcelain veneer cast metal crown.

In addition, the present invention may be used with any conventionaltooth margin preparations such as: chamfer, shoulder, chamfer bevel,shoulder bevel, knife edge and feather edge. The margin may also bereinforced if desired. The porcelain jacket crown may also be reinforcedif desired. The porcelain jacket crown prepared in accordance with thepresent invention will have an almost invisible metal line at thegingiva. An even further distinct advantage of the present inventionlies in the reduction in the weight of the metal in a jacket crown ofthe present invention which is only 20 to 30 milligrams.

Accordingly, it is the principle object of the present invention toprovide a porcelain jacket crown having a high resistance to fracturecomparable with or even greater than the conventional porcelain veneercast metal crown.

Another object of the present invention is to provide a preformed copingfor forming the porcelain jacket crown of the present invention.

An even further object of the present invention is to provide a methodfor constructing a jacket crown.

Further objects and advantages of the present invention will becomeapparent from the following detailed description of the invention whenread in conjunction with the accompanying drawings of which:

FIG. 1 is an enlarged perspective of a segment of the preferred metalfoil starting material of the present invention in its preferredcircular geometry;

FIG. 2 is a perspective of a dental coping prepared in accordance withthe present invention from the metal foil starting material of FIG. 1;

FIG. 3 is a transparency in perspective of the dental coping of FIG. 2in the initial stage of being molded to a die of the prepared tooth;

FIG. 4 is another transparency in perspective of the dental coping inFIG. 3 in its final stages of being adapted to the die of the preparedtooth; and

FIG. 5 is an illustration in perspective of the dental coping of FIG. 3as a standing structure after having been adapted to the die.

Referring now to FIG. 1 in which a metal foil segment 10 is shownrepresenting the starting material for preparing the jacket crown inaccordance with the present invention. The metal foil segment 10 ispreferably circular in geometry and composed of a thin foil metalsubstrate 12 of platinum or another high fusing temperature metal and athin coated layer 14 superimposed on the foil metal substrate 12. Thecoated layer 14 should be of a noble metal based composition preferablywith gold as its major constituent. There are numerous gold basedcompositions shown to those skilled in the dental arts for use in thepreparation of a dental restoration and upon which a veneering materialsuch as porcelain may be fired. The preferred composition of the coatedlayer 14 should have a relatively low melting temperature characteristicand contain at least 50% gold with one or more of the following elementsin combination: silver, palladium, platimum, iridium, copper andaluminum. A conventional binder may be added to the composition so thatit may spread more readily over the platinum foil substrate 12 to formthe coated layer 14. The coated layer 14 should form a bonded matrixwith or without the application of heat which has the physicalproperties of being flexible, malleable and spongy. The gold basedcomposition should have a low temperature fusing characteristic suchthat it flows after sufficient heat is applied for reasons which will beexplained in greater detail hereafter.

The thickness of the platinum foil substrate 12 should be in the rangeof between 15 to 50 microns with an optimum thickness of 25 to 27microns. The thickness of the gold based layer 14 should be between 10to 50 microns and preferably between 20 to 25 microns.

The metal foil segment 10 is preferably round although any geometry maybe used in which multiple folds may be made which will partially overlapone another when adapted to a die as hereinafter explained. When themetal foil segment 10 is circular its diameter for a typical die isbetween about 22 to 28 mm.

The metal foil segment 10 of FIG. 1 is folded into a predeterminedgeometrical shape having a multiple number of fold lines 18 as shown inFIG. 2 for forming the dental coping 16 of the present invention. Themultiple fold lines 18 may be formed by hand or by machine. Thetechnique or mechanism employed to perform the folding operation is notcritical to the present invention. It is the arrangement of multiplefold lines in a predetermined array to form multiple flaps or pleatswhich forms the underlying theory in the preparation of a jacket crownin accordance with the present invention.

An example of a hand folding operation that may be used for forming apreferred arrangement of fold lines 18 from the metal foil segment 10involves placing the metal foil segment 10 over one end of a cylindricalsupport bar (not shown) and squeezing the segment 10 into fold lines 18using the thumb and forefinger of one hand while holding the segment 10in place over the support bar. In such case each fold line 18 willradially extend from a central unfolded area 20. The central unfoldedarea 20 will conform in dimension to the support bar upon which it wasplaced in forming the fold lines 18. The diameter of the unfolded areais not significant provided it is small relative to the total area ofthe segment 10.

Another hand folding operation simply involves folding the segment 10 inhalf and then in quarters until the desired number of fold lines 18 areformed. This is a somewhat less desirable procedure since the fold lineswill extend radially from a central point or apex without forming anunfolded area 20 in the center of the segment 10. It should however beunderstood that forming an unfolded area 20 is not critical to theinvention.

The fold lines 18 form substantially triangular like flaps or pleats 22with a curved base line 24 shown as a straight line in FIGS. 2 and 3 forsimplicity. Each triangular angular like flap 22 has two fold lines 18with a common fold line 18 between adjacent pairs. The number of flaps22 that should be formed may vary with four to sixteen being preferredand with eight being the optimum number for most typical jacket crownpreparations.

The preferred geometry of the dental coping 16 includes a multiplenumber of fold lines 18 which radially extend from a centrally locatedunfolded area 20 in an arrangement which form triangular-like flaps 22.The dental coping 16 should preferably be modified to include aplurality of small slotted openings 26. These openings 26 may be made asan integral part of the manufacturing operation of the dental coping 16or as part of the procedure of the dental technician in the preparationof the jacket crown as will hereinafter be explained in greater detail.The slotted openings 26 are slits formed in the segment 10 preferablyalong the fold lines 18. Neither the position of the slotted openings26, their size or number are critical. Their primary function is toprovide access for the noble metal composition to flow to the undersideor uncoated surface of the platinum foil substrate 12 when heat isapplied to the finished coping 16 during the final preparatory step inthe preparation of a jacket crown.

FIGS. 3-6 illustrate the preferred sequence of steps in the preparationof a jacket crown in accordance with the present invention. Thepreformed coping 16 is placed over a die 28 of a prepared tooth with theunfolded area 20 seated upon the top or occlusal end 29 of the die 28.The die 28 is conventionally prepared from an impression of the preparedtooth and is a replica thereof. The unfolded area 20 facilitatescentering the dental coping 16 over the die 28 and makes the coping 16easier to adapt to the die 28 as is more readily apparent from FIG. 4.

Each of the flaps 22 are wrapped tightly around the die 28 in a uniformclockwise or counter clockwise oriented sequence resulting in anarrangement of overlapping flaps 22 as shown in FIG. 4. The coping 16should also extend over the gingival margin 31. The die 28 and coping 16is then placed in a swaging device (not shown) or pressure is applied byhand to adapt it to the die 28. The coping 16 is then removed from thedie leaving a free standing structure 33 as shown in FIG. 5. Heat isthen applied to the free standing structure 33 by placing it over theflame of a bunsen burner for between five to thirty seconds based onflame temperature until the structure 33 gets cherry red and shiny.Alternatively the free standing structure 33 can be placed in a furnaceand sintered at a temperature of about 1020° to 1070° C. until the sameresult is achieved. The low fusing preferably gold based composition ofthe metal layer 14 will flow through the slotted openings 26 to form acompact matrix between the foil substrate 12 and the gold basedcomposition on the undesirable thereof without any air pockets.

After the heating step, porcelain can be directly applied in aconventional manner to form the jacket crown of the invention. It ishowever desirable but not essential, to coat the outside surface of thefree standing foil structure 33 using a bonding composition to achievean unbreakable bond between the porcelain layers and the foil structure33. A preferred bonding composition is disclosed in a copending U.S.patent application Ser. No. 171,255 entitled Bonding Material and MethodFor Bonding A Ceramic To A Nobel Based Metal, and now abandoned, thedisclosure of which is herein incorporated by reference. The bondingmaterial disclosed in this application includes a nobel based metalcomposition in combination with a halide of a noble metal preferably anoble metal halide. The bonding material must be sintered to the foilstructure 33 at a temperature above 1600° F. This can be achievedsimultaneously with the firing of the required porcelain outer layers.Any number of porcelain layers may be applied and fired for forming thejacket crown of the invention. Generally, three or more layers ofvarying dental porcelain composition starting with an opaque layer arebuilt up and fired at temperatures in a range from about 1600° to 1820°F. Before firing the final glaze the area below the gingival margin iscut and the porcelain shaped and finished to the correct gingival marginfor the prepared tooth.

After the final glaze the crown is ready to be inserted into the mouthand cemented to the tooth using any conventional dental cementcomposition. It is suggested practice to roughen the interior of thecrown i.e. the unerside of the inner substrate layer 12 before the crownis cemented to the tooth. The roughness maybe achieved by sand blasting.

Although the invention was described in connection with the applicationof porcelain for forming a porcelain jacket crown it is equallyapplicable to the use of any polymer veneering material such asconventional dental acrylics in substitution of the porcelain ceramicmaterial for the superstructure of the jacket crown.

What we claim is:
 1. A .[.jacket.]. .Iadd.dental .Iaddend.crowncomprising a composite body .[.including.]. .Iadd.formed from .Iaddend.athin foil of high fusing temperature metal having a surface geometryconforming to a die to which it has been adapted .[.with the foil havingat least a minimum of three folded over pleats with each pleat forming atriangular like flap in the unfolded position,.]. a thin coating of a.[.noble.]. .Iadd.gold .Iaddend.based .Iadd.noble .Iaddend.metalcomposition superimposed over one surface of said .[.thin metal foil anddisposed beneath the folded over pleats.]. .Iadd.high fusing temperaturemetal with said composite body having a plurality of folded oversections which radially extend from an axis through the center of thefoil in a symmetrical arrangement about the center of the foil.Iaddend.and a relatively thick outer coating of a dental veneeringmaterial.
 2. A .[.jacket.]. .Iadd.dental .Iaddend.crown as defined inclaim 1 wherein said folded over .[.pleats overlap one another.]..Iadd.sections constitute pleated sections with each pleated sectionrepresented by fold lines which form a triangular like flap in theunfolded position.Iaddend..
 3. A .[.jacket.]. .Iadd.dental.Iaddend.crown as claimed in claim 2 wherein said thin foil is composedof platinum and wherein said veneering material is fired on dentalporcelain.
 4. A .[.jacket.]. .Iadd.dental .Iaddend.crown as claimed inclaim 2 wherein said .[.noble.]. .Iadd.gold .Iaddend.based .Iadd.noble.Iaddend.metal composition comprises at least 50% gold and at least oneof the following elements selected from the group consisting of: silver,palladium, iridium, copper and aluminum.
 5. A .[.jacket.]. .Iadd.dental.Iaddend.crown as claimed in claim 4 wherein the weight of said noblebased metal in said jacket crown is between about 20 to 30 milligrams.6. A dental coping for a .[.jacket.]. crown restoration comprising athin foil of high fusing temperature metal .[.arranged in a prefoldedgeometrical configuration having at least a minimum of three pleatedsections with each pleated section represented by fold lines which forma triangular like flap and a coating of a noble based metal compositionsuperimposed upon the surface of said thin foil over said pleatedsections.]. .Iadd.having a thin gold based noble metal compositiondisposed upon the surface of said thin foil with said thin foil arrangedin a prefolded geometrical configuration having a plurality ofoverlapping sections.Iaddend..
 7. A dental coping as defined in claim.[.6.]. .Iadd.20 .Iaddend.wherein each .[.pleated section is of a sizesuch that upon folding it will overlap an adjacent pleated section.]..Iadd.section is pleated and represented by fold lines which form atriangular like flap in the unfolded configuration..Iaddend.
 8. A dentalcoping as defined in claim .[.7.]. .Iadd.6 .Iaddend.wherein said thinfoil was circular in shape before folding.
 9. A dental coping as definedin claim 8 wherein said fold lines radially extend from an unfolded areasubstantially in the center of said coping with the unfolding area beingsmall compared to total area of the foil.
 10. A dental coping as definedin claim 9 wherein said thin foil is composed of platinum.
 11. A dentalcoping as defined in claim 10 further comprising a plurality of smallslotted opening arranged about the periphery of said coping.
 12. Amethod of forming a dental .[.jacket.]. crown comprisingpreparing a thinmetal foil of high fusing temperature metal into a substantiallycircular substrate; coating one surface of the foil substrate with anoble based metal composition having a low fusing temperature of belowabout 1070° C.; forming a multiple number of fold lines in said coatedfoil substrate with each two adjacent fold lines substantially defininga triangular like flap; mounting said coated foil substrate over a dieof the prepared tooth with the coated surface exposed; partiallyoverlapping each flap about said die in a clockwise or counterclockwisesequence with the foil tightly wrapped about said die; adapting saidtightly wrapped foil to said die; removing said die for providing aninner structure for said jacket crown; heating said inner structureabove the low fusing temperature of said noble based metal composition;and coating a veneering material over said inner structure.
 13. A methodas claimed in claim 12 further comprising the step of forming smallslotted openings about the periphery of said coated foil substratefollowing the folding step.
 14. A method as claimed in claim 13 whereinsaid slotted openings are formed along the fold lines.
 15. A method asclaimed in claim 14 wherein said veneering material is a fired onprocelain.
 16. A method as claimed in claim 15 wherein said heating stepis performed by placing said inner structure under the flame of a bunsenburner for between 5 to about 30 seconds. .Iadd.
 17. A method of forminga dental coping for a dental crown comprising the steps of forming athin foil metal composite of a high fusing temperature metal and asuperimposed low fusing temperature metal, prefolding said foil to forma plurality of foldable sections which radially extend from an area inthe center of the foil adapted to be mounted over the occlusal surfaceof the tooth to be restored in a symmetrical arrangement with respect tothe center of the foil, folding the sections over, adapting saidcomposite foil to a die of the tooth to be restored, removing saidcomposite foil from said die and heating said composite foil to atemperature above the low fusing metal temperature so as to cause saidlow fusing temperature metal to melt for forming a compact matrixbetween said high fusing temperature metal layer, the folded oversections of foil, and the melted gold based low fusing temperaturemetal. .Iaddend. .Iadd.18. A method as defined in claim 17 wherein saidcomposite body is heated by subjecting it to the flame of a bunsenburner or in a furnace at a temperature of about 1020° C. to 1070° C..Iaddend. .Iadd.19. A method as defined in claim 18 wherein the foldedover sections of said composite body are folded to overlap one another..Iaddend. .Iadd.20. A dental coping as defined in claim 9, wherein saidfolded over sections overlap. .Iaddend.